Process for preparation of carboxylic acids



PROCESS FOR PREPARATION OF CARBOXYLIC ACIDS Filed Dec. 8, 1955 ACID FORMED, MILLEQUIVALENTS HOURS INVENTORS' TRUMAN P. MOOTE, JR. ALFRED STEITZ, JR.

BY M 21 ATTORN Y United States atent 2,823,216 Patented- Feb. 1 1, 1058 ice Truman P. Moote, Jr., and Alfred Steitz, Jr., Tulsa, Okla., assignors to Pan American PetroleumCorporation,- a corporation of Delaware Application December 8, 1955, Serial No. 551,912 14 Claims. (Cl.260--41:3)

The present invention relates to a novel process for the preparation of higher molecular weight acids... More particularly, it pertains to the manufacture of, such'acids by reacting an olefin with a relatively low molecular. weight carboxylic acid in the liquid phase,

It has been previously disclosed. thatzethylenecan be made to react with carboxylic acidstoproduce. an .acid having from three to thirteen carbon .atoms, however,.in such work only a relatively small percentage. of the. final product acid was composed of one. molecule. of.react-. ing acid and one molecule of ethylene. Inmostcases the major part of the reaction product, i..e.,.75. to.80 percent, was composed of one molecule of reacting acid and two or more molecules of ethylene..- In some instances telomerization of ethylene occurred to.such..an extent that appreciable quantities otthe .reaction.prod.-. ucts were of greaseor lard-like consistency, Apparent: ly, under the reaction conditions afforded by the prior art the hydrocarbon portion adding on to the acid tended to undergo extensive telomerization.

It' is an object of our invention to provide a method for the preparation of relatively high molecular weight carboxylic acids from primary olefins and low molecular weight carboxylic acids ranging from three to about eight carbon atoms. It is another object of our invention to produce addition products of said olefins and low molecular weight acids in which such products have an average. molecular. weight ranging fromabout 116 to about 250. It is a still further object to provide conditions favoring theformation, in predominating amounts, of a reaction product that is a 1:1 adduct of acid to olefin, i. e., a product acid. in which the total number of carbon atoms present is. equal to the sum of the carbonatoms present in the-acid and olefin from which saidproduct acid .wasderived. It is still a further ob ject ofour invention to provide conditions whereby acid production proceeds at a relatively high rate with outlowering the proportionof the aforesaid 1:1 adduct formed The reaction iselfected under conditions which favor the formation of free radicals whichv in turn serve as..a catalyst, or initiator, for the. principal reaction. As is already known theseradicals can be formed, for example, by exposure of the reactants to ultraviolet light, by the addition of a suitable peroxide such as for example diacetyl, ditertiary-butyl or benzoyl peroxides. Also, variousether peroxides may be employed. Since the means by which the reaction of our invention is catalyzed forms no part thereof and since techniques for effecting such conditions of catalysis are well-known we shall hereafter refer to such conditions, where appropriate,.as free radical forming conditions. Ordinarily, if a peroxide is used as the free radical former it is employed in molar ratios ranging from about 1:5 to about 1:15, i. e., peroxide to low molecular weight acid; preferably in the neighborhood of about 1:10. In cases Where ultraviolet light is used as a means for providing 2 free radical formingconditions we employ; a light source having a wave length lessthanabout 3000 A., typically 500 to about 2900.A..and preferably from about 2000 to 2500 A. Since ordinary glass or Pyrex .type glass serves as a filter for lightrays below about..3000 A., lamp envelopes made .of'such glass should be removed prior to use. The envelope or covernext to'the sourceshould be of quartz or other suitable light transmitting:

material. such as, for example, calcium fluoride through which rays of desiredwave :length can pass.-- In prac-- tice we have found that! a-quartz ultraviolet lamp in-- serted into a suitableuwellalso constructed of quartz. serves as a satisfactory means for generating light of the required wave length.- Since the reaction occurs in. the liquid phase, the section of the quartz well contain-- ing the ultraviolet light should be submerged. This ar-- rangement is used when initiating the reaction with an: arc lamp which operates most efficiently at about 500 C. However, a resonance lamp can be submerged in; the reaction mixture without using a quartz well. Its.

temperature for maximum efliciency is about 55 C- For a given quantity of acid product we have found that; the amount of ultraviolet .light required varies with the: molar ratio of reacting acid to olefin employed. The. effect of varying such molar ratio in accordance with the process of our invention will be discussed in greater detail below.

The temperature at which our invention is to be carried out will in general vary with the olefin used. Ordinarily it is preferred to operate at temperatures of from about 15 to 25 C. below the boiling point of the olefin up to about its boiling point, or the reflux temperature of the reaction mixture. However, when a peroxide is employed as the free radical initiator the reaction temperatures are necessarily limited to the decomposition temperature of the peroxide. Generallyspeaking, however, for the range of olefins contemplated it may be said that the reaction temperature to be employed in carrying out our invention may range-from about 30 to about 200 C. at atmospheric pressure. This boil ing range includes primary olefins or l-alkenes ranging from l-pentene to about l-octadecene. Olefins suchas propylene and l-butylene may also be employed under conditions where .they exist in. the. liquid. state. Thus, with propylene the reaction temperature can not exceed 91 C. (the critical temperature thereof). At that temperature the pressure required to maintain ,propylenein the liquid phase is about- 675 p. s. i. For l-butylene the critical temperature is C. and the pressure required at that temperature for liquid phase operation is about 630 p. s. i.

The carbonv chain in which the olefin linkage, appears: may be either straighter branched; however, .the olefin linkage itself should be primary, i. e., it should have the structure:

wherein R is a hydrocarbon residue.

The acids to be employed as reactants in the process of. our invention are relatively low in molecular weight;

From the standpoint of both rapid conversion and pro duction of the 1:1 adduct of acid to olefin, previously mentioned, we have found that more favorable results in this regard are secured when. the acid and olefin. are reacted in a molar ratio of at least :1 and preferably in a molar ratio of at least about 1. Also the use of a suitable solvent such as toluene, benzene, xylene, and the like, and/or lower temperatures, i. e., 1025 C. below the boiling point of the reaction mixture may tend to favor formation of the aforesaid 1:1 adduct in predominating amounts. Also, when employing ultraviolet light as the free radical initiator we have found that the formation of radicals increased by first eliminating certain impurities from the acid which cause it to darken when exposed to ultraviolet light for extended periods of time. This has been found to be true when the acid is initially water white. Thus, in practice, prior to reacting the acid with an olefin in accordance with our invention, we subject the acid itself to radiation with ultraviolet light. By

' Table I Reaction Mole ratio Rate of Acid Run No. Time, hrs. 0; acid/ Production, a octene meq./hr.

this treatment impurities present which tend to darken Curves A, B and C of the above-mentioned drawing on prolonged exposure to the light rays in the ultraviolet show the rates of product acid formation when employwave band are rendered less volatile. The resulting radiing starting ratios of propionic acid to l-octene of 0.1, ated acid is distilled and the distillate acid is found to be 1.0 and 10, respectively. From these results it is obvious quite reactive when subsequently subjected to the condithat acid to olefin ratios as low as 1:1 are undesirable. tions of our invention. In some instances we have made In fact ratios below 5:1 do not appear promising. In runs with acids purified in the manner just described and curve D (run #4) the l-octene was dropped continuously with unpurified acids from the same batch. In the case into boiling propionic acid at the rate of about 0.07 mole of the runs in which purified acids were used we found per hour and the resulting molar ratio of propionic acid that the acid formation rate was approximately five times t0 Octene decreased from infinity down to about six. faster than that observed in the case of the unpurified ma- From these results it is Seen that high 3110s of reacting terial. These color forming impurities apparently include acid to Olefin e desirable Under Conditions Similar to carbonyl components. They may be removed by means those given above the use of ditel'tiary-butyl Peroxide, of a preliminary treatment of the acid with an aqueous Q Y Peroxide and other P PfifOXideS in a P 0 bisulfite or hydroxylamine solution, a water wash or per- 35 mm) of 9 of olefin i yields results slmllar culation through charcoal, silica gel, extraction of an to those glven aboveaqueous solution of the acid salts with a light hydrocar- EXAMPLE H bon or ethyl ether followed by regeneration of the acids a from their salts in a known manner, etc. i The reactants listed in thetable below were employed The process of our invention may be further illustrated 40 in a series of eight different runs. In all cases the reaction by the following specific examples. Reference is first was effected at approximately the reflux temperature of made to the curves of the accompanying drawing which the reaction mixture. Proportions of reactants, type of shows the effect of reactant molar ratios on rate of acid ultraviolet light source employed and the duration of each formation. The data on which these curves are based run are given in the table.

Table II Reactants Product Acids Neutral Equivalent; Distil- Distribution, Mol React. M01 Ratio, lation Percent of- 1 Run N0. Acid Primary Time, Acid] U. V. Lamp, Temper- Pressure, Cut Uncor- Cor- Olefin Hrs. Olefin Type ure, mm. Hg rected rectcd C. for for Hydro- Hydro- 1:1 1:2

carbon carbon Adduct Adduct Hexene 30 10.0 Are"; g; it? agg g? 158 do. 113 10.6 Resonance- 136 61 gg fi gi Octane 98 855 372 25 100 ltii iij: {iii 53% -37 "as do 72 1.0 Arc do so 1010 .do do 30 9.9 .....do.......{ He rene" 30 V 10.0 do

1 9% hydrocarbon. 1 70% hydrocarbon. v 3 This product contained at least two moles of olefin to one of acid.

was obtained under the conditions stated in Example 1 below.

EXAMPLE I A series of four runs, was made in which the reaction was carried out at the reflux temperature of a mixture of l-octene and propionic acid, i. e... about C. A Gen- 76 distribution of product acid is about 75-85 mole percent of the 1:1 adduct composed of 1 mole of reacting acid and 1 mole of olefin) and about 15-25 mole percent of the 1:2 adduct. At a starting ratio of 1 mole of acid to 1 mole of olefin the distribution of product acid is about 25-30 mole percent 1:1 adduct and 70-75 mole percent of the 1:2 adduct. Actually, as the neutral equivalents indicate in the above table, the products obtained from a reaction mixture having reacting acid and olefin present in a ratio of about 1:1 possess a high hydrocarbon content. This indicates that under such circumstances the olefin itself polymerized and the resulting polymcntogether with product acid, passed overhead as distillate.

In view of the foregoing description, numerous variations of the process of our invention will be apparent to those skilled in the art. Fundamentally, our invention contemplates the reaction, in the liquid phase, of a primary olefin with carboxylic acids of the type described above to produce a product consisting primarily of a carboxylic acid having a total number of carbon atoms equivalent to the sum of the carbon atoms in the reacting acid and olefin. Accomplishment of such a result in the presence of free radical forming conditions is considered to lie within the scope of our invention.

We claim:

1. In a process for the preparation of organic acids from a primary olefin and an aliphatic carboxylic acid, the improvement which comprises producing at least about mole percent of acarboxylic acid product in which the molar ratio of olefin to the reacting acid is 1:1' by reacting in the liquid phase a primary olefin having from 5 to 18 carbon atoms with an aliphatic carboxylic acid under free radical forming conditions, said acid and olefin being present in the reaction mixture in a molar ratio of at least about 10:1 and at a temperature ranging from about 15 to about 25? C. below the boiling point of the olefin up to about the reflux temperature of said reaction mixture at about atmospheric pressure.

2. The process of claim 1 in which the olefin employed contains from five to eighteen carbon atoms and the reacting carboxylic acid contains from three to seven carbon atoms.

3. The process of claim 2 in which the olefin employed contains from five to eight carbon atoms.

4. The process of claim 2 wherein the free radical forming conditions are produced by means of an organic peroxide.

5. The process of claim 2 wherein the free radical forming conditions are produced by means of ultraviolet light having a wave length of less than 3000 A.

6. The process of claim 5 in which the wave length of the ultraviolet light employed ranges from about 500 to 2900 A.

7. The process of claim 5 in which the ultraviolet light employed has a wave length ranging from 2000 to 2500 A.

8. The process of claim 4 in which the organic peroxide is di-tertiary-butyl peroxide.

9. The process of claim 4 in which the organic peroxide is benzoyl peroxide.

10. The process of claim 2 in which the olefin is 1- hexene and the carboxylic acid is propionic acid.

11. The process of claim 2 in which the reacting acid is a butyric acid and the olefin is l-octene.

12. The process of claim 2 in which the reacting acid is hexanoic acid and the olefin is l-hexene.

13. The process of claim 2 in which the reacting acid is propionic acid and the olefin is l-octene.

14. The process of claim 5 in which the color forming impurities present in the aliphatic carboxylic acid are removed prior to reaction with said olefin.

References Cited in the file of this patent UNITED STATES PATENTS 2,402,137 Hanford et a1. June 18, 1946 2,433,015 7 Roland et a1. Dec. 23, 1947 2,585,723 Banes et al. Feb. 12, 1952 

1. IN A PROCESS FOR THE PREPARATION OF ORGANIC ACIDS FROM A PRIMARY OLEFIN AND AN ALIPHATIC CARBOXYLIC ACID, THE IMPROVEMENT WHICH COMPRISES PRODUCING AT LEAST ABOUT 70 MOEL PERCENT OF A CARBOXYLIC ACID PRODUCT IN WHICH THE MOLAR RATIO OF OLEFIN TO THE REACTING ACIDS 1:1 BY REACTING IN THE LIQUID PHASE A PRIMARY OLEFIN HAVING FROM 5 TO 18 CARBON ATOMS WITH AN ALIPHATIC CARBOXYLIC ACID UNDER FREE RADICAL FORMING CONDITIONS, SAID ACID AND OLEFIN BEING PRESENT IN THE REACTION MIXTURE IN A MOLAR RATIO OF AT LEAST ABOUT 10:1 AND AT A TEMPERATURE RANGING FROM ABOUT 15* TO ABOUT 25*C. BELOW THE BOILING POINT OF THE OLEFIN UP TO ABOUT THE REFLUX TEMPERATURE OF SAID REACTION MIXTURE AT ABOUT ATMOSPHERIC PRESSURE. 